This project will focus on how growth factors and the activation of the MARK pathway control intracellular[unreadable] Ca2+ in intact cells and will suggest a molecular basis for the specific roles for nuclear and cytosolic Ca2+[unreadable] signaling and the importance of the regulation of these effects on the growth and function of hepatocytes.[unreadable] Three isoforms of the InsPSR have been identified. The cellular localization of each receptor isoform may be[unreadable] correlated with its functional properties. In hepatocytes the InsPSR type 1 isoform (lnsP3R-1) is cytosolic[unreadable] whereas the type 2 isoform (lnsP3R-2) is found throughout the cell, but is predominantly found in the nucleus[unreadable] and the canalicular region. We hypothesize that in hepatocytes MKP-1 differentially regulates the function[unreadable] and distribution of the InsPSR. In this project the interplay between the InsPSR and MAP kinases will be[unreadable] tested on the activity of single InsPSR channels, the ability of isolated cells to generate transient changes in[unreadable] intracellular Ca2+, and the dynamics of InsPSR distribution. An understanding of these complex interactions[unreadable] is necessary to explain the molecular mechanisms of Ca2+ signaling and thus the regeneraton of liver.[unreadable] The hypotheses to be tested include 1) Does activation of MAPK alter the function of the InsPSR and[unreadable] intracellular Ca2+ signaling? 2) Does MKP-1 inactivation of MAPK alter the function of the InsPSR and[unreadable] intracellular Ca2+ signaling? and 3) Does MAPK phosphorylation modulate the InsPSR isoform distribution[unreadable] within the cell?[unreadable] The preliminary results presented here show for the first time that the InsPSR of hepatocytes are regulated[unreadable] by the MAPK pathway The experiments outlined in this project will investigate the functional of this[unreadable] regulation of the InsPSR at the single channel level and will correlate the channel properties with cell and[unreadable] organ function. The results to be obtained will identify regulatory factors that determine isoform-specific[unreadable] Ca2+ signaling responses, how the cell regulates the channel isoforms to optimize cellular responses, and[unreadable] how this regulation goes awry in pathophysiological situations, such as liver degeneration and regeneration.[unreadable] A long term goal will be to use the molecular information obtained in these studies to suggest useful[unreadable] treatments for individuals affected with liver disease.